feat(payment): standalone ZarinPal broker on pay.flatrender.ir

A generic multi-client payment gateway so FlatRender, meezi.ir and
bargevasat.ir can all pay through ZarinPal's single verified callback
domain (pay.flatrender.ir).

New Go service services/payment (clones the notification skeleton +
vendored deps):
- migration 31_payment_broker.sql — `payment` schema: client_apps,
  transactions, webhook_deliveries.
- ZarinPal v4 client ported from the proven identity PaymentService
  (request.json -> StartPay -> verify.json; codes 100/101).
- client API: POST /v1/pay/request + /v1/pay/inquiry, authed by
  X-Api-Key + HMAC body signature; GET /callback/zarinpal (the single
  verified endpoint) verifies, then 302s the user back to the site's
  return_url (signed) and fires a signed, retried webhook.
- per-client ZarinPal merchant override (default = shared merchant);
  amount stored canonically in Rial, unit to ZarinPal env-configurable.
- admin API /v1/admin/* (FlatRender admin JWT): client-app CRUD +
  key issue/rotate + transactions list.

Deploy wiring: payment-svc in docker-compose.v2.yml (host port 1607),
pay.flatrender.ir server block in mirror-nginx conf, ENV_FILE +
README updates (cert SAN + manual migration note).

Admin UI: src/components/admin/PaymentsAdmin.tsx (client apps with
one-time key reveal + rotate, transactions table) + /admin/payments
page + nav link + fa/en strings; pay-admin proxy route to payment-svc.

Docs/SDK: deploy/PAYMENTS.md (integration contract) + deploy/sdk/flatpay.js
(zero-dep Node client + webhook verifier) for meezi/any site.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

services/payment/vendor/github.com/leodido/go-urn/makefile

@@ -0,0 +1,51 @@
+SHELL := /bin/bash
+RAGEL := ragel
+GOFMT := go fmt
+
+export GO_TEST=env GOTRACEBACK=all go test $(GO_ARGS)
+
+.PHONY: build
+build: machine.go
+
+.PHONY: clean
+clean:
+	@rm -rf docs
+	@rm -f machine.go
+
+.PHONY: images
+images: docs/urn.png
+
+.PHONY: snake2camel
+snake2camel:
+	@cd ./tools/snake2camel; go build -o ../../snake2camel .
+
+.PHONY: removecomments
+removecomments:
+	@cd ./tools/removecomments; go build -o ../../removecomments .
+
+machine.go: machine.go.rl
+
+machine.go: snake2camel
+
+machine.go: removecomments
+
+machine.go:
+	$(RAGEL) -Z -G1 -e -o $@ $<
+	@./removecomments $@
+	@./snake2camel $@
+	$(GOFMT) $@
+
+docs/urn.dot: machine.go.rl
+	@mkdir -p docs
+	$(RAGEL) -Z -e -Vp $< -o $@
+
+docs/urn.png: docs/urn.dot
+	dot $< -Tpng -o $@
+
+.PHONY: bench
+bench: *_test.go machine.go
+	go test -bench=. -benchmem -benchtime=5s ./...
+
+.PHONY: tests
+tests: *_test.go
+	$(GO_TEST) ./...